This disclosure relates to methods for manufacturing memory devices, as for example carbon-based resistive memory devices including non-volatile memory cells. Also carbon-based resistive memory elements, devices and integrated circuits are presented.
Memory devices are widely used in computing applications and in many electronic devices. For some applications, non-volatile memory which retains its stored data even when power is not present, may be used. For example, non-volatile memory is typically used in digital cameras, portable audio players, wireless communication devices, personal digital assistants, and peripheral devices, as well as for storing firmware in computers and other devices.
A variety of conventional memory technologies have been developed. For example, non-volatile memory technologies are flash memory, magneto-resistive random access memory (MRAM), and phase change memory (PCM). Due to the great demand for memory devices, researchers are continually improving memory technology and developing new types of memory, including new types of non-volatile memory and memory based on new materials. It is generally desirable to reduce the dimensions of the memory cells and reduce the complexity of peripheral circuitry used to operate the memory.
To increase the efficiencies of electronic devices their size is constantly being reduced. For memory devices, conventional technologies, such as flash memory and DRAM, which store information based on storage of electric charges, may reach their scaling limits in the foreseeable future. Additional characteristics of these technologies, such as the high switching voltages and limited number of read and write cycles of flash memory, or the limited duration of the storage of the charge state in DRAM, pose additional challenges. To address some of these issues, researchers are investigating memory technologies that do not use storage of an electrical charge to store information. One such technology is resistivity changing memory, which stores information based on changes in the resistivity of a memory element. Depending on the resistivity changing memory technology being used, the resistivity of the storage layer is typically switched between a low resistivity state and a high resistivity state through the application of voltage or current across the storage layer.
One conventional type of resistivity changing memory or resistive memory is known as phase change memory (PCM). The resistivity changing memory elements used in PCM are phase changing memory elements that include a phase changing material. The phase changing material can be switched between at least two different crystallization states (i.e., the phase changing material may adopt at least two different degrees of crystallization), wherein each crystallization state may be used to represent a memory state. When the number of possible crystallization states is two, the crystallization state having a high degree of crystallization is also referred to as “crystalline state”, whereas the crystallization state having a low degree of crystallization is also referred to as “amorphous state”. Different crystallization states can be distinguished from each other by their differing electrical properties, and in particular by their different resistances. For example, a crystallization state having a high degree of crystallization (ordered atomic structure) generally has a lower resistance than a crystallization state having a low degree of crystallization (disordered atomic structure).
Usually, the phase changing material forming the storage layer of a conventional PCM consist of a chalcogenide compound material, such as GeSbTe (GST), SbTe, GeTe or AgInSbTe. Programming the PCM is mostly executed by a temperature change of the phase changing material. There are a variety of mechanisms to realize such a thermally induced phase change. Conventional PCM relies on specific materials that may pose difficulties in the manufacturing of memory cells.